(1) Field of the Invention
The present invention pertains to a process for removing iron oxide scale from the surfaces of processed sheet metal. In particular, the present invention pertains to an apparatus and method of removing scale from the surfaces of processed sheet metal that employ high pressure jets of water directed from nozzles positioned in close proximity to the sheet metal surfaces.
(2) Description of the Related Art
Processed sheet metal is sheet metal that has been prepared for use in making cold rolled sheet metal, and for use in manufacturing some goods. Sheet metal of this type is used in the manufacturing of goods that require a thicker gauge steel, for example agricultural equipment, automotive parts, steel containers, bed frames, etc.
Before sheet metal is used by manufactures it is typically prepared by a hot rolling process. During the hot rolling process, carbon steel is heated to a temperature in excess of 1,500° F. (815° C.). The heated steel is passed through successive pairs of opposing rollers that reduce the thickness of the steel sheet. Once the hot rolling process is completed, the processed sheet metal or hot rolled steel is reduced to ambient temperature, typically by quenching it in water, oil, or a polymer liquid, all of which are well known in the art. The processed sheet metal is then coiled for convenient storage and transportation to the ultimate user of the processed sheet metal, i.e. the manufacture of aircraft, automobiles, or home appliances, etc.
During the cooling stage of processing the hot rolled sheet metal, reactions of the sheet metal with oxygen in the air and the moisture involved in the cooling process can result in the formation of an iron oxide layer, or scale as it is commonly referred to, on the surfaces of the sheet metal. The rate at which the sheet metal is cooled and the total temperature drop from the hot rolling process effects the amount and composition of scale that forms on the surface during the cooling process.
Before the sheet metal can be used by the manufacture, the surface of the sheet metal must be conditioned so that the sheet metal can be painted or otherwise coated, and the sheet metal provides a smooth exterior surface of the product being manufactured. The most common method of removing oxide from the surface of hot rolled or processed sheet metal before coating the sheet metal surfaces is a process known as “pickle and oil”. In this process of removing oxide, the sheet metal, already cooled to ambient temperature following the hot rolling process, is uncoiled and pulled through a bath of hydrochloric acid to chemically remove the scale formed on the sheet metal surfaces. Following removal of the scale by the acid bath, the sheet metal is then washed, dried, and immediately “oiled” to protect the surfaces of the sheet metal from oxidation or rust. The oil provides a film layer barrier to air that shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture. It is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture.
The “pickle and oil” process is effective in removing substantially all of the oxide layer or scale from processed sheet metal. However, the “pickle and oil” process has a number of disadvantages. For example, the acid used in the acid bath of the sheet metal is an environmentally hazardous chemical which has special storage and disposal restrictions. In addition, the acid bath stage and subsequent oiling stage of the sheet metal “pickle and oil” process requires a substantial area in the manufacturing facility of the sheet metal.
Thus, there is a need in the industry for an improved apparatus and method for surface conditioning processed sheet metal by removing oxide or scale from the surfaces of the sheet metal that does not require the manufacturing floor space of the prior art “pickle and oil” process, and does not require the use of a hazardous chemicals such as in the “pickle and oil” process.